1. Field of the Invention
The present invention relates to the field of wellbore drilling, and more particularly to the cleaning of wellbores after a drilling operation is complete. The present invention provides an improved apparatus and method for collecting and removing debris left in the wellbore after the drilling operation.
2. Description of the Related Art
During wellbore cleaning operations debris within the well is removed from the casing wall and flushed out by circulating drilling mud. However, debris will often remain in the well when completion fluid displaces the drilling mud and consequently a filtration tool may be deployed to capture this remaining debris. In deviated or horizontal wells, the filtration tool will not capture all of the remaining debris as some of the debris will have settled on the low side of the wellbore casing away from the main fluid stream. In many wellbore completions the cleanliness of the wellbore is crucial, either due to the type of completion or the properties of the associated reservoir. Debris remaining on the low side of the casing is therefore unacceptable, as a relatively empty filter tool can give a false impression of the cleanliness of the wellbore.
One solution to this problem has been to maximise the flow rates within the wellbore during the cleaning operation. However, this solution increases the cost of the operation due to the additional energy consumption by the pumps to generate the increased flow. It is also only partly successful as debris picked up by the increased flow may still settle back down on the low side of the casing in deviated or horizontal wells.
An alternative solution is to employ one or more impellers which are non-rotatably fixed to the drill string, where rotation of the drill string will rotate the impeller(s) and agitate or disturb the debris off the low side of the casing and into the circulating fluid flow out of the well. However, as with the increased flow rate solution, the debris can return to the low side of the casing if it moves towards the outside of the flow on the way along the well.
It is an aim of the present invention to obviate or mitigate the disadvantages of these existing cleaning apparatus and methods.